The present invention relates to methods and devices that make it possible to evaluate the potential of the skin, including the lips, for scavenging free radicals, said potential also being referred to as “antioxidant potential.”
Harmful free radicals are molecules that have a very short half-life, in the range 1 nanosecond (ns) to 1 millisecond (ms), and that are therefore very unstable and very reactive.
It is known that the ability of the skin to protect itself from external aggression such as exposure to ultraviolet rays, pollution, or other types of biological or chemical aggression, can depend in particular on its epidermal content of non-enzymatic antioxidants that are capable of scavenging the free radicals.
Thus, vitamin E is a known antioxidant for protecting the skin and for preventing it from aging, and it is often found in cosmetic formulations.
Depending on the individual, the concentration in the skin of antioxidants such as molecules with a thiol group, ascorbate, tocopherol, tocotrienol, uric acid, vitamin A, ubiquinone 10, spermine, and the like can vary, e.g. depending on age, skin type, diet, degree of exposure to ultraviolet rays, etc.
At present, common apparatus for monitoring free radicals directly is exceedingly expensive.
It has been proposed to use neutral sensor molecules called spin-trap that react to give radical-like molecules that are more stable and thus measurable by Electron Spin Resonance (ESR).
The formation of lipid peroxides or of squalene peroxides as indicators of cutaneous stress has been studied in the publication “Ultraviolet A induces generation of squalene monohydroperoxide isomers in human sebum and skin surface lipids in vitro and in vivo”: S. E. Mudiyanselage, M. Hamburger, P. Elsner, J. J. Thiele, J. Invest. Dermatol. June 2003; 120(6) 915-22, and in German patent application DE 10 164 553.
The article “Evaluation of free radical scavenger effects of Helianthus annus extract using new ex vivo stripping methods,” P. Mondon and al. in “Cosmetics, aerosols & toiletries” in Australia May 20, 1999, describes a method consisting in taking a sample of the stratum corneum, and in extracting therefrom the antioxidants the reaction of which with a colored reagent that is 1,1-Diphenyl-2-Picryl-Hydrazyl (DPPH) is carried, the bleaching of the reagent being monitored using a spectrophotometer at 517 nanometers (nm).
DPPH is a stable free radical, which, in the presence of one or more radical scavengers, loses its free radical character with a reduction in its color.
As a result of its stable character, DPPH has also been used in Electron Paramagnetic Resonance (EPR) techniques for measuring the free radical scavenger activity of the human epidermis, as described in the article “HPLC analysis of vitamin E isoforms in human epidermis: Correlation with minimal erythema dose and free radical scavenger activity”: J. Fuchs, S. Weber, M. Podda, N. Groth, T. Herrling, L. Packer, R. Kaufmann, Free radic. Biol. Med. Feb. 1, 2003; 34 (3): 330-6.
Current analysis techniques implementing DPPH remain relatively complex and costly.